There is an ongoing need for vehicle tires having improved treads for use in driving in slippery conditions, such as over snow. Such treads can improve not only traction, but also handling characteristics and control, and braking of the vehicle.
While a number of grooved tire treads for use in this service are already known, none have been developed with a substantial increase in outward facing surface area of the groove or grooves defined by tire tread elements. For example, U.S. Pat. No. 5,647,926 discloses a “winter” tread having circumferentially spaced tread blocks offset from each other, each of which has a plurality of transverse sipes and similarly shaped transverse grooves which define the boundaries of the tread elements. Thus, the circumferential grooves of the tread are defined by repeatedly irregular walls. A number of prior art patents, typified by U.S. Pat. No. 5,535,798 and U.S. Pat. No. 2,843,172, show straight walled circumferential tread grooves with so-called reentrants formed on one or both walls and the bottom of the groove, which reentrants increase in width and depth toward the bottom of the groove. U.S. Pat. No. 5,386,861 discloses full depth projections 20 formed extending inward from the groove wall sides 10 of the tread blocks (FIG. 1), forming, in effect, a groove of decidedly irregular surface(s). The projections are at an even steeper angle with respect to the tread surface than are the groove sidewalls (FIG. 2). At least some of projections 20 also have additional saw-tooth-like sub-projections 32 (FIGS. 3 & 4).